Well then that tailor is a fool because even with the side seams taken in on a shirt there can be excess cloth at the lower and middle back. All it is is shaping, some alterations tailors would do well to stop foisting their own preferences and whims onto clients.

Find a tailor/seamstress/shirtmaker with a lot of experience tapering shirts. Try on the shirt in his/her presence and
have it pinned to your liking before it is altered by taking in the side seams, adding darts or both.

Find a tailor/seamstress/shirtmaker with a lot of experience tapering shirts. Try on the shirt in his/her presence and
have it pinned to your liking before it is altered by taking in the side seams, adding darts or both.